use `EngineApi` from `alloy`

[rnbguy]

I feel the methods in this file are obsolete

https://github.com/informalsystems/emerald/blob/main/engine/src/engine_rpc.rs

because alloy-provider already offers them under engine-api feature.

https://docs.rs/alloy-provider/latest/alloy_provider/ext/trait.EngineApi.html